1. Field of the Invention
The present invention relates to a lateral insulated gate bipolar transistor.
2. Summary of the Prior Art
An insulated gate bipolar transistor (hereinafter referred to as an IGBT) has, for example, a semiconductor substrate serving as a drift region, which substrate is of a first conductivity type (e.g. is of n-type). A base region of different conductivity type (e.g. p-type) is formed in one surface of the substrate, and an emitter region of the same conductivity type as the substrate is formed within the base region. A collector region may then be formed in the opposite surface of the substrate, which collector region is of the same conductivity type as the base region. Emitter electrodes are provided on the emitter region, which emitter electrodes also contact the base region. A collector electrode is provided on the collector region. A gate electrode structure, formed by a gate electrode and an insulating film, is provided which contacts the base region, the emitter region and the drift region.
When a positive potential is applied to the gate electrode of such an IGBT, the surface of the base region under the insulating film is inverted to n-type conductivity, thereby forming a channel. In this case, when the collector electrode has a higher potential than the emitter electrode, electrons move from the emitter region to the collector region through the channel and drift regions. The electrons that reach the collector region promote the injection of holes from the collector region. This decreases the resistance of the drift region, due to conductivity modulation. Thus, the structure is similar to a MOSFET in which the collector region is changed into a drain region. However, the resistance of the IGBT in the on state is lower than that of the equivalent MOSFET.
When fabricating such a device, it is inconvenient for the collector region to be formed on the opposite surface of the substrate from the other regions, and therefore it has been proposed to form a IGBT with a lateral structure, in which the base, emitter and collector regions are in the same surface of the substrate, so that the electrodes may also be on a common surface of that substrate. An example of such a lateral insulating gate bipolar transistor is shown in U.S. Pat. No. 4,933,740.
In U.S. Pat. No. 4,933,740, a plurality of such lateral insulated-gate bipolar transistors are formed together in an array, with adjacent transistors being mirror images of each other. Thus, for a given transistor, the adjacent transistor on one side has its emitter region in common with the given transistor, while the adjacent transistor on the other side has its collector region in common with the given transistor. The emitter and collector electrodes of the transistors of the array may then be integral, so that they are electrically connected. Furthermore, the emitter and collector electrodes of each transistor are elongate.